Compact fluid heat exchanger

ABSTRACT

A tubular type heat exchanger having two vertical header tanks with one of the header tanks having fluid inlet and outlet fittings on opposite ends. A partition separates the interior of this header tank into an inlet portion and an outlet portion. Ushaped tubes extend in a horizontal direction between the tanks, passing fluid from the inlet portion of the first tank to the interior of the second header tank and then back to the outlet portion of the first tank. Individual rectangular fins are brazed to the tubes in planar relation for spacing the tubes horizontally and vertically. The edges of the rectangular collar members are separated a predetermined distance from corresponding edges of adjacent collar members for preventing binding engagement therebetween when the collars thermally expand in response to exposure of fluid having a temperature of about 2,500*F. Vertical retention rods which extend adjacent the tubes have pins engaging the underside of the tubes for supporting the tubes vertically while simultaneously preventing distortion of the tubes in a horizontal direction normal to the tube&#39;&#39;s axis.

[ Sept. 17, 1974 COMPACT FLUID HEAT EXCHANGER [75] Inventor: James R. Mondt, Pontiac, Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: July 27, 1972 [21] Appl. No.: 275,715

Related US. Application Data [63] Continuation-in-part of Ser. No. 228,207, Feb. 22,

1972, abandoned.

[52] US. Cl 165/81, 122/510, 165/162, 165/163, 165/176 [51] Int. Cl F281 7/00 [58] Field of Search 165/176 X, 162 X, 172, 165/82; 122/510, 163 X, 81

[56] References Cited UNITED STATES PATENTS 1,769,963 7/1930 Price 165/81 1,907,867 5/1933 Potter 165/172 X 2,007,309 7/1935 Sengstaken 165/176 X 2,142,367 1/1939 Morgan 165/81 X 2,736,400 2/1956 Gay et a1. 165/81 2,867,416 l/1959 Lieberherr 165/176 X 3,361,538 1/1968 Hess 122/356 X 3,526,274 9/1970 Gardner 165/81 X 3,554,168 1/1971 Woebcke. 165/162 X 3,675,710 7/1972 Ristow 165/176 X Primary Examiner-Albert W. Davis, Jr. Assistant Examiner-S. J. Richter Attorney, Agent, or Firm-K. H. MacLean, Jr.

[5 7] ABSTRACT A tubular type heat exchanger having two vertical header tanks with one of the header tanks having fluid inlet and outlet fittings on opposite ends. A partition separates the interior of this header tank into an inlet portion and an outlet portion. U-shaped tubes extend in a horizontal direction between the tanks, passing fluid from the inlet portion of the first tank to the interior of the second header tank and then back to the outlet portion of the first tank. Individual rectangular fins are brazed to the tubes in planar relation for spacing the tubes horizontally and vertically. The edges of the rectangular collar members are separated a predetermined distance from corresponding edges of adjacent collar members for preventing binding engagement therebetween when the collars thermally expand in response to exposure of fluid having a temperature of about 2,500F. Vertical retention rods which extend adjacent the tubes have pins engaging the underside of the tubes for supporting the tubes vertically while simultaneously preventing distortion of the tubes in a horizontal direction normal to the tube s axis.

2 Claims, 4 Drawing Figures l COMPACT FLUID HEAT EXCHANGER This application is a continuation-in-part of Ser. No. 228,207, filed on Feb. 22, 1972, now abandoned.

This invention relates to tubular heat exchangers and means to support the tubes vertically while preventing lateral distortion of the tubes.

Tubular heat exchangers may be used in a variety of applications. The present heat exchanger was developed as a steam generator for a steam engine powered vehicle. Because the temperature of the combustion gas which produces the steam approaches 2,500F., the tubes are subjected to very severe thermal distortions caused by elongation of the tubular structure as well as lateral displacement of the tube.

The present heat exchanger freely permits thermal expansion and contraction of the tubes in an axial direction to prevent the formation of stresses on the brazed joints between the tubes and the header tanks. In a preferred embodiment, the tubes are U-shaped and extend in horizontal planes between vertical header tanks. The tubes are vertically stacked one above the other to form columns of tubes which are spaced from each other by rectangular fins brazed to the tubes. The fins permit axial movement of the tubes in response to thermal expansion while at the same time maintaining the spacing between the tubes. Vertical retention rods extend adjacent the stacked columns to prevent lateral movement of the tubes. Pins which project from the retention rod extend beneath the tubes to support them in a vertical direction. The rods prevent the tubes from moving laterally in a horizontal or vertical direction. The individual brazed fins and the retention rods maintain horizontal and vertical spacing of the tubes while permitting axial expansion.

In steam generation applications, it has been found that tubular type heat'exchangers with water or steam within the tubes is preferable to the fire-tube type heat exchanger with combustion gases in the tube and water and steam outside the tube. This is partially because a fire-tube type steam generator requires relatively large pressure vessel for the steam. Also, the pressure drop of the combustion gas in the tubes is undesirably large. With the water in the tubes, the pressure vessel can be relatively small. However, unless the tubes are quite large or many tubes are used in parallel, the steam pressure drop can be undesirable. Consequently, the present steam generator utilizes many parallel tubes extending between a first header tank and a second header tank. This provides a very compact heat exchanger with a small pressure vessel volume and a small pressure drop in the steam lines.

Therefore, an object of the present invention is to provide a tubular type heat exchanger particularly suited for high temperature applications such as a steam generator which is exposed to relatively hot combustion gases.

A further object of the present invention is to provide a tubular type heat exchanger having a plurality of tubes extending between header tanks which are adapted to pass fluid from an inlet portion of one header tank through a portion of the tubes to the other header tank and then back through the remainder of the tubes to an outlet portion of the first header tank.

A still further object of the present invention is to provide a tubular heat exchanger with horizontally extending tubing between header tanks which are spaced from one another by coplanar fins brazed to the tubes and which are vertically supported and laterally restrained by vertical retention rods.

Further objects and advantages of the present invention will be apparent from the following detailed de scription, reference being had to the accompanying drawings in which a preferred embodiment is clearly shown.

IN THE DRAWINGS:

FIG. 1 is an elevational view of the present tubular heat exchanger;

FIG. 2 is a horizontal sectional view of the heat exchanger taken along section line 2-2 in FIG. 1 and looking in the direction of the arrows;

FIG. 3 is a vertical sectional view of the heat exchanger shown in FIG. 1 taken along section line 33 and looking in the direction of the arrows; and

FIG. 4 is a vertical sectional view of the heat exchanger shown in FIG. 1 taken along section line 44 and looking in the direction of the arrows.

In the drawings, a heat exchanger 10 is illustrated. The heat exchanger 10 includes first and second vertically extending header tubes or tanks 12 and 14. The tanks 12 and 14 are tubular in construction having their ends covered by plug members 16. The plugs 16 are attached to the header tanks l2, 14 by brazing or welding. An inlet fitting l8 and outlet fitting 20 are attached to the ends of the first header tank 12 to form an inlet passage 22 and an outlet passage to the interior of the header tank 12. An inlet coupling 26 is threadably secured at 28 by a nut 30 which engages the inlet fitting 18. Coupling 26 is adapted to be connected to a source of fluid to be heated. Likewise, an outlet coupling 32 is connected to the outlet fitting 20 at threaded portion 34 by a nut 36.

The interior of header tank 12 is separated by a partition or wall 38 which is attached to the header tank 12 by brazing or welding at 40. Partition or wall 38 forms an inlet portion 42 and an outlet portion 44 within the tank interior.

A plurality of U-shaped tubes 46 extend in a horizontal direction between the header tanks 12 and 14. Each U-shaped tube 46 includes two parallel portions 48 which are interconnected at one end by a curved portion 50, 50 and are fluidly connected at the other ends 52 to the interiors of the tanks 12 and 14. The tubes are attached to the header tanks by brazing or welding. The horizontal U-shaped tubes 46 are vertically stacked as best shown in FIG. 1. Also, the tubes 46 are connected to tanks 12, 14 in a staggered fashion as is illustrated in FIGS. 2 and 3. This produces two columns of vertically stacked tubes 48 and 48'. Combustion gases from a turbine exhaust or the steam generator burner flow through the alternately staggered tubes 46 in the direction indicated by arrows 54 in FIGS. 2 through 4.

The parallel portions 48 and 48 of the tubes 46 are horizontally and vertically spaced from one another by rectangular fins 56 which are brazed or otherwise attached to the tubes as is best shown in FIG. 4. The fins 56 are attached to the tubes 46 at any predetermined distance from the curved ends 50, 50' of tubes 46 so that all fins are planar. Thus, as the tube portions 48 expand or contract with temperature variations, the fins 56 remain in a substantially planar relationship with one another to space the tubes horizontally and vertically.

Retention rods 58 extend vertically adjacent the linear portion of the stacked tubes 46. Pins 60 are connected to the vertical rods 58 and extend beneath the tubes 46 to support the tubes in a vertical direction. The uppermost pins 62 are curved over the upper tube 46 and the lower tube 46 shown in FIG. 3 rests upon a cross arm or pin 64 connected to the rod 58. The rods 58 are attached to a surrounding duct means (not shown) which channels hot combustion gases from a combustion chamber to the tubes. The hot combustion gases may develop temperatures in the range of 2,500F. at the inlet face of the heat exchanger. This high temperature will create large thermal deflections of the U-shaped tubes in an axial and radial direction. The combination of the vertical retention rods 58 and individual fins 56 support the tubes in a vertical direction and also prevent distortion of the tubes in a lateral direction normal to the axis of the tube while simultaneously permitting axial expansion of the linear portions of the tubes. This unrestrained expansion of the tubes in an axial direction prevents thermal distortions from stressing the brazed joints between the tubes and the header tanks.

When the tubular heat exchanger is used as a steam generator in a steam powered vehicle, the heat exchanger is located across the flow of combustion gas in a duct from the outlet of the combustion chamber. The hot combustion gases flow over the U-shaped tube 46 in paths indicated by the arrows 54. Water is passed through the inlet 22 and into the inlet portion 42 of header tank 12. It then flows through the upper portion of U-shaped tubes 46 in FIG. 1 and into the interior of the second header tank 14. It then flows through the lower tubes 46 and into the outlet portion 44 of the first header tank 12. Between the inlet portion and the outlet portion of the heat exchanger, the water is heated and transformed into high pressure steam.

Starting a steam powered vehicle engine involves many operations. A cold start is defined as a start when the outlet temperature of the steam generator is less than 200F. First, the steam generator is filled with water by activating an electric transfer pump. The combustion chamber is then ignited and the water in the steam generator begins to rise in temperature and pressure. After the pressure rises above 600 psig, excess steam is vented to the condenser of the system to hold the 600 psig pressure until warm up is completed. When a steam superheat temperature is reached of about 700F. at 800 psia, the expander (engine) is activated. This start up procedure has been found to occupy approximately 2 minutes. During this start up period, the steam generator is subjected to unusually great thermal stresses due to the rapid temperature rise.

In one embodiment of a steam generator, a multipass unit was tested having four banks of tubes between the gas inlet side and the gas outlet side. First, an economizer section consisting of about 40 tubes in two rows was located at the gas inlet side. These tubes were formed of 316 stainless steel tubing having a diameter of about 0.375 inches and a two wall thickness of about 0.035 inches.

Adjacent to the economizer section, a superheat portion of the generator was located having about 40 tubes in two rows of about tubes per row. The same 0.375 inch 316 stainless steel tubes were used. The superheat portion of the steam generator was subjected to slightly cooler exhaust gases than the economizer section because of the heat absorbed by the economizer. The third section or bank of the steam generator was a boil section consisting of 72 tubes in six rows of about 12 tubes per row. The same 316 stainless steel tubing was used for this section as for the economizer and superheat sections. Next to the boil section was located a second portion of the economizer, first mentioned, consisting of about 48 tubes in four rows of about 12 tubes per row. This second economizer portion was finned to extract a maximum amount of the remaining heat from the combustion gases as it is discharged from the heat exchanger.

This first embodiment of the steam generator did not include the inventive use of individual spacing fins and retention rods. Although this steam generator was satisfactory for a limited period of time, the front portion (near the gas inlet face) was subjected to severe thermal distortions which caused the tubes to deflect laterally a substantial amount. This deflection was severe enough to prevent the maintenance of the desired spacing between tubes for efficient gas flow over and around the tubes.

A second steam generator was built and tested. It eliminated the economizer at the gas inlet side of the steam generator. A superheat portion was placed at the gas inlet side which included about 28 tubes in two rows with about 14 tubes per row. lncoloy, type SP 163 tubing with about a 0.375 inch diameter and a wall thickness of 0.035 inches was utilized. Next to the superheat portion of the steam generator, a boil section was located which included about tubes in six rows of about 15 tubes per row. Adjacent the boil section, a finned section was located having about 30 tubes in two rows of about 15 tubes per row. Finally, at the gas outlet side of the steam generator, an economizer section was placed having about 62 finned tubes. This second embodiment utilizes rectangular fins brazed to the tubes for vertical and horizontal spacing and vertical retention rods to prevent lateral displacement of the tubes. The spacing between adjacent rectangular fins in this particular embodiment is approximately 10/ 1000ths of an inch when the heat exchanger is at room temperature. Extensive testing of this second embodiment produced satisfactory long term operation without lateral distortion of the tubes or failure of the brazed joints between the tubes and the header tank.

While the embodiment illustrated in the drawings and described in the above application is a preferred embodiment of a particular heat exchanger, other embodiments may be adapted.

What is claimed is as follows:

1. A tubular type heat exchanger comprising:

elongated first and second header tanks extending vertically adjacent one another in substantially parallel relation; inlet and outlet fittings on opposite ends of the first of said header tanks for the passage of fluid into and out of the heat exchanger; partition means in the interior of said first header tank dividing said header tank into an inlet portion and an outlet portion; a plurality of U-shaped tubes extending in generally horizontal planes between said tanks; each U-shaped tube having parallel elongated portions interconnected at one end by a curved portion, with the other ends of elongated portions being integrally joined to said first and second header tanks, respectively to resist relative bending movement therebetween, whereby fluid flows from said inlet portion of said first header tank through a portion of said U-shaped tubes into the interior of said second header tank and then through another portion of said U-shaped tubes to the outlet portion of said first header tank; said parallel elongated portions of said tubes being stacked in vertical columns; the elongated portions of alternate tubes extending from said header tank from an elevational view being offset horizontally from upper and lower adjacent elongated portions, thereby forming spaces between said tubes to produce an undulating fluid pass; individual collar members having a rectangular shape attached to each elongated portion of said U-shaped tube and being in substantial coplanar relationship to one another when said tubes are at a uniform temperature; the edges of said rectangular collar members being separated a predetermined distance from corresponding edges of adjacent collar members for preventing binding engagement therebetween when said collars thermally expand in response to exposure of fluid having a temperature of about 2,500 F.; said coplanar collar members being lo cated adjacent said free ends of said U-shaped tubes to space said elongated tube portions; said collar separation being sufficient to prevent binding engagement between said individual collar members to allow individual and unequal axial movement of said elongated tube portions caused by nonuniform temperature exposure of said tubes to fluid.

2. A tubular steam generating heat exchanger comprising: elongated first and second header tanks vertically extending adjacent one another in substantially parallel relation; inlet means on one end of said first header tank fluidly connected to a source of water; outlet means on the other end of said first header tank fluidly connected to a power producing steam expander; partition means in the interior of said first header tank dividing it into an inlet portion and an outlet portion; aligned U-shaped tubes extending in generally horizontal planes between said tanks; each U-shaped tube having parallel elongated portions interconnected at one end by a curved portion, the other ends of the elongated portions being attached to said first and second header tanks respectively, whereby water flows from the inlet portion of said first header through a portion of said U-shaped tubes into the interior of said second header tank and then through another portion of said U-shaped tubes into the outlet portion of said first header tank during which passage the water is transformed into steam; registered individual collars attached to said elongated portions of said tubes in coplanar relationship to one another; said collars when the unit is at a relatively cold temperature defining vertical and horizontal gaps in relation to each other and when the unit is at a relatively high temperature abutting each other so as to space said tubes horizontally and vertically with respect to each other while simultaneously permitting relative V axial movement of said elongated portions of said tubes caused by hot combustion gases flowing around said tubes; vertical retention members rigidly mounted and extending adjacent said vertical columns of tubes to prevent lateral movement of said tubes in a radial direction which would be caused by hot combustion gases around said tubes; horizontal members extending from said vertical rods beneath said elongated tube portions for supporting said tubes in a vertical direction.

' l =l= =l= 

1. A tubular type heat exchanger comprising: elongated first and second header tanks extending vertically adjacent one another in substantially parallel relation; inlet and outlet fittings on opposite ends of the first of said header tanks for the passage of fluid into and out of the heat exchanger; partition means in the interior of said first header tank dividing said header tank into an inlet portion and an outlet portion; a plurality of U-shaped tubes extending in generally horizontal planes between said tanks; each U-shaped tube having parallel elongated portions interconnected at one end by a curved portion, with the other ends of elongated portions being integrally joined to said first and second header tanks, respectively to resist relative bending movement therebetween, whereby fluid flows from said inlet portion of said first header tank through a portion of said U-shapeD tubes into the interior of said second header tank and then through another portion of said U-shaped tubes to the outlet portion of said first header tank; said parallel elongated portions of said tubes being stacked in vertical columns; the elongated portions of alternate tubes extending from said header tank from an elevational view being offset horizontally from upper and lower adjacent elongated portions, thereby forming spaces between said tubes to produce an undulating fluid pass; individual collar members having a rectangular shape attached to each elongated portion of said U-shaped tube and being in substantial coplanar relationship to one another when said tubes are at a uniform temperature; the edges of said rectangular collar members being separated a predetermined distance from corresponding edges of adjacent collar members for preventing binding engagement therebetween when said collars thermally expand in response to exposure of fluid having a temperature of about 2,500* F.; said coplanar collar members being located adjacent said free ends of said U-shaped tubes to space said elongated tube portions; said collar separation being sufficient to prevent binding engagement between said individual collar members to allow individual and unequal axial movement of said elongated tube portions caused by nonuniform temperature exposure of said tubes to fluid.
 2. A tubular steam generating heat exchanger comprising: elongated first and second header tanks vertically extending adjacent one another in substantially parallel relation; inlet means on one end of said first header tank fluidly connected to a source of water; outlet means on the other end of said first header tank fluidly connected to a power producing steam expander; partition means in the interior of said first header tank dividing it into an inlet portion and an outlet portion; aligned U-shaped tubes extending in generally horizontal planes between said tanks; each U-shaped tube having parallel elongated portions interconnected at one end by a curved portion, the other ends of the elongated portions being attached to said first and second header tanks respectively, whereby water flows from the inlet portion of said first header through a portion of said U-shaped tubes into the interior of said second header tank and then through another portion of said U-shaped tubes into the outlet portion of said first header tank during which passage the water is transformed into steam; registered individual collars attached to said elongated portions of said tubes in coplanar relationship to one another; said collars when the unit is at a relatively cold temperature defining vertical and horizontal gaps in relation to each other and when the unit is at a relatively high temperature abutting each other so as to space said tubes horizontally and vertically with respect to each other while simultaneously permitting relative axial movement of said elongated portions of said tubes caused by hot combustion gases flowing around said tubes; vertical retention members rigidly mounted and extending adjacent said vertical columns of tubes to prevent lateral movement of said tubes in a radial direction which would be caused by hot combustion gases around said tubes; horizontal members extending from said vertical rods beneath said elongated tube portions for supporting said tubes in a vertical direction. 